Has the U.K. become a tax haven?

U.S. firms are increasingly eyeing up London for takeover targets to benefit from low U.K. corporate tax rates.

U.S. companies are increasingly viewing the U.K. as a place to relocate to pare their tax bills.

Why? Relatively low tax rates and a business-friendly environment.

Pfizer(PFE) was the latest high-profile example; it tried to take over the British pharmaceutical firm AstraZeneca(AZN).

American and French media giants Omnicom(OMC) and Publicis(PGPEF) also planned a mega-merger that would have seen the new firm domiciledin the U.K., though the deal was scuppered.

Meanwhile, the British-based InterContinental Hotels(IHG) was reportedly approached by a U.S. suitor who may have been looking to take advantage of a more favorable U.K. tax system.

British corporate tax rates are near 20%. In the U.S., rates are closer to 40% -- among the highest in the developed world.

The U.S. also levies high taxes on income that's earned abroad and brought back -- or repatriated -- to the States.

The U.K. rules are not as strict, allowing money to flow home without so many tax hassles, said Gary Hufbauer, a senior fellow at the Peterson Institute for International Economics.

"The basic point is that the U.S. corporate tax system is the most onerous amongst the advanced countries," Hufbauer said. About $1.6 trillion in foreign earnings have been left overseas to avoid U.S. taxes, he added.

But moving to the U.K. is not as simple as opening an office in London and telling authorities your tax base has changed. The U.S. has blocked this strategy, so a corporate takeover is required.

Today, a U.S. company can only really move to a more tax-friendly nation through a process known as "inversion," where acquisition activity leads a foreign partner to own more than 20% of the stock in the merged entity, among other requirements.

This rule has spurred U.S. companies to consider big British takeover plans, but it's also created a backlash in Washington.

But various proposals in Congress to make it harder for companies haven't advanced. Meantime,companies are scrambling to make a move, said Kevin Phillips, an international tax partner at accounting firm Baker Tilly in London.

"People are trying to get in before the door gets shut," he said. "While the opportunity is there, people are taking the chance."

Other companies have passed over the U.K. entirely in favor of even more tax-friendly places.

The U.S. banana producer Chiquita Brands International(CQB) has plans to go to Ireland, where corporate tax rates are about 12.5%. Chiquita agreed to take over Ireland's Fyffes, and the newly merged company will put its legal headquarters in Ireland.

Other countries that are known for low corporate taxes are Switzerland, Singapore and Luxembourg. On the other hand, most companies veer away from France because of its historically high taxes.